What meta tags are available?

Meta tags provide a means of adding extra information about your HTML document.
This is information that either your browser might be able to make use of or typically
to provide additional information to search engines.

There are two types of meta tags:

<meta name="tag" content="data">

and

<meta http-equiv="tag" content="data">

Information provided by http-equiv is passed to the browser before
it receives the rest of the document. It provides information that could therefore
affect how the browser handles the document. Both styles of meta tags must be positioned
within the head of the document (i.e. between the <head> and
</head> tags).

META NAME tags

Meta name tag

Description

Author

The name of the author of the page.

Copyright

Allows a copyright statement to be embedded.

Description

A short description of the page. Used by search engines as a summary
description of the page.

It is generally recommended to keep the meta-description to no more than
150 characters, anything longer risks it being truncated by a search
engine. However the exact length limit will vary between search engines.

If you need to include double quotes in the description then escape them,
for example:

<meta name="description" content="A &quot;cool&quot;
tip">

gives the description: A "cool" tip

Generator

The name of the tool used to create the page. (Unsure how useful this
is to web-authors.)

Keywords

Used by search engines to index the page. Use to specify keywords of
relevance to the page.

Robots

Gives instructions to web-robots (also called web-bots). Be aware that
the web-bot is free to ignore it! The CONTENT portion should
be a comma separated list of one or more of the following:

noindex

Do not index the page. Unless "NOFOLLOW" is
also specified then any links on the page may still be followed.

nofollow

Do not follow any links that are on the page.

noimageindex

Do not index any of the images on the page.

noimageclick

Do not index links to images on the page, instead use a
link to the page.

noodp

Do not use titles or descriptions from the Open Directory Project
(DMOZ). Otherwise where the
page is listed in DMOZ the search engine, if DMOZ aware (such as google), might choose to use the
description in DMOZ rather than what it gleans from the page.

nosnippet

Do not show the description (or extract) of the page in
search engine results.

noarchive

Do not take a cached copy of the page. This does not
stop the page from being listed, but should stop the search
engine from taking a copy of the page.

For example to prevent a page from being indexed:

<meta name="robots" content="noindex">

these tags can be combined so, for example, to prevent a page from being
indexed and any links followed:

<meta name="robots" content="noindex, nofollow">

In addition there are some robots options which are recognised only by
specific search engines. The following (by its nature) may not be complete:

In addition to the above set of "standard" meta name tags, there are some
which are recognised only by specific search engine bots. The following list may
is not complete but does include the most significant bots:

Meta name tag

Used by

Description

googlebot

Google

Use the same settings as for name="robots",
but applied only to the google-bot.

slurp

Yahoo!

Use the same settings as for name="robots",
but applied only to the Yahoo bot - which is called "Slurp"..

msnbot

MSN, Live Search, Bing

Use the same settings as for name="robots",
but applied only to the Microsoft Msn-Bot, which in turn feeds into MSN,
Live Search and Bing.

There are also some meta tags which are recognised by many mobile devices:

Meta name tag

Description

viewport

Specifies the intended size when viewing on a mobile device.
Orignally created by Apple for the mobile Safari browser, it has now
been widely adopted as the de-facto standard.

The CONTENT portion should
be a comma separated list of one or more of the following:

width=320

Specify the logical width of the viewport, in pixels. In this
case 320 pixels wide.

width=device-width

Logical width should be the physical number of pixels across the
display.

height=480

Logical height of the viewport in pixels. In thise case 480
pixels.

height=device-height

Logical height of the display should be the physical number of
pixels vertically across the display.

user-scalable=yes|no

Whether the user can zoom in and out. Supports yes or no,
default is yes.

initial-scale=1.0

Set the initial zoom. In this case 1.

maximum-scale=2.5

Maximum limit for zooming/scaling. Must be in the range 0.25 to
10.

minimum-scale=0.5

Minimum limit for zooming/scaling. Must be in the range 0.25 to
10.

MobileOptimized

Supported by some Windows mobile browsers. The content specifies the
width of the browser window. For example:

<meta name="MobileOptimized" content="320">

HandheldFriendly

Supported by BlackBerry browser.

<meta name="HandHeldFriendly"
content="true">

Specifies that the content is optimised for mobile devices. For those
devices that support viewport, this is
similar in effect to:

HTTP-EQUIV tags

HTTP-EQUIV tags that are not recognised (i.e. supported) by the browser will
be silently ignored (i.e. the viewer will not see an error). So you can use HTTP-EQUIV
tags safely without worrying too much whether a given browser will support them.

Meta name tag

Description

Content-Type

Specifies the character encoding scheme used for the document. A semicolon
(;) can be used to combine values.

Typical values:

content="text/html"

Standard HTML.

content="text/html; charset=ISO-8859-1"

Standard HTML, character set is ISO-8859-1, which is the standard
for Western Europe and is also the normal browser default.